Flexible antenna for a wireless radiation dosimeter

ABSTRACT

A flexible antenna for a wireless X-ray dosimeter chip is described. The flexible antenna includes a dipole antenna associated with an artificial magnetic conductor, wherein the artificial magnetic conductor includes: a top layer configured to partially act as a reflective surface; a bottom conductive ground plane layer configured to prevent propagation of incident electromagnetic waves and to reflect the electromagnetic waves; and a middle layer including a foam material configured to provide an appropriate phase delay between incident electromagnetic waves from the top layer and the reflected waves from the ground plane layer.

1. FIELD OF THE INVENTION

The present invention relates generally to medical sensors, and moreparticularly, to a dipole antenna structure for use in a wirelessdosimeter tag for biomedical applications.

2. DESCRIPTION OF RELATED ART

Recent research initiatives for biomedical applications have addressedthe design of flexible and wearable medical devices for early diseasedetection and prevention health monitoring and reduction of invasivemedical procedures. This has created an increasing demand for flexible,conformal, compact, low-power wireless power transfer (WPT) modules thatare easy to fabricate, low-cost and maintain efficient performance ondiverse host structures.

The key component in the design of these wireless modules is the antennastructure. The literature reports the use of flexible materials such asconductive fabrics and polydimethylsiloxane (PDMS) substrate, liquidmetal and paper to achieve conformity. The aforementioned demands havealso inspired the use of additive technologies like inkjet printing toachieve flexible and robust antenna designs for use with everydayclothing, wearable sensors, biomedical wireless sensors and radiofrequency identification (RFID) systems.

Biomedical applications not only require conformal antenna structuresbut more importantly, antenna designs that maintain efficientperformance on a human body, as in, or in the presence of body tissuesfor in-vivo applications. Amongst a few others, these designs haverevealed that the human body and body tissues negatively impact antennaperformance due to their high permittivity, thereby acting as lossystructures. For these scenarios, where the antenna calls for someisolation from its environment or host, there is ongoing research onmetamaterials acting as high impedance surfaces (HIS) as a means ofrealizing thinner and light weight antennas and even improved antennagain, as demonstrated in the prior art. HIS structures are periodicstructures acting as frequency selective surfaces (FSS) to control thepropagation of electromagnetic waves. They can act as artificialmagnetic conductors (AMC) by reflecting incident waves without phasereversal at a specific frequency; the incident waves see a highimpedance surface (open circuit) at the design frequency, mimicking aperfect magnetic conductor (PMC), and permitting efficient radiation forantennas placed parallel and close to the surface.

A number of sensors having a variety of functionalities for the targetedapplication have been reported in the prior art. These include passiveand active circuit designs. For example, US Patent Application,US2010/0096556A1 to Langis Roy et al. discloses a miniaturized floatinggate metal-oxide semiconductor field-effect transistor (FGMOSFET)radiation sensor. The sensor preferably comprises a matched pair ofsensor and reference FGMOSFETs wherein the sensor FGMOSFET has a largerarea floating gate with an extension over a field oxide layer, foraccumulation of charge and increased sensitivity.

Several patents have been issued on color changing indicators, monitors,detectors, and dosimeters for monitoring a variety of biomedicalprocesses. For example, US patent application, US 2011/0168920 A1 toYoder et al. discloses a device comprising a dosimeter for measuring oneor more doses of radiation; and an RFID tag comprising an antenna forcommunicating with an RFID tag reader and non-volatile memory forstoring data therein. This disclosure utilizes an optically stimulatedluminescence (OSL) sensor that includes a reference filter material andis used to adjust the dose determined by the reference sensor at verylow energies of x-rays or gamma rays.

For example, U.S. Pat. No. 7,652,268 to Patel et al. discloses a generalpurpose dosimeter reader for determination of a radiation dosage, basedon comparison of an image of a treated dosimeter with a series of imagesof a pre-treated dosimeter. The dosimeter undergoes a color changeproportional to the dosage. The sensor may have more than one indicatorof the same or different classes. The color change may be a gradualcolor development or intensification; a gradual color fading: a gradualcolor change or an abrupt color change.

For example, U.S. Patent Application US2015/0116093A1 to Swagerdiscloses method of detecting a stimulus that can include detecting anoutput from a radio frequency identification tag including a sensor. Thesensor portion is configured to change resistivity when the stimuluscontacts or interacts with the radio frequency identification tag,whereby the resistivity change alters the output of the radio frequencyidentification tag, wherein the radio frequency identification tagincludes a carbon nanotube or multiple carbon nanotubes.

For example, the French Patent Application, FR2945128A1 discloses adosimeter for use during a radiotherapy treatment session, which has aprinted circuit board wrapped in an envelope forming material, and ametal-oxide semiconductor field-effect transistor (MOSFET) placed onprinted circuit board. A RFID (radiofrequency identification device) toidentify the dosimeter using an electronic device such as a memory chipcontaining data and capable of using an antenna to transmit informationto a reader is also disclosed. The RFID device may be integrated to theprinted circuit board or retrofitted thereon.

Presently blood products are irradiated in chambers using X-ray orgamma-ray sources to prevent transfusion associated graft versus hostdisease (TA-GvHD). Typically, blood product irradiation is identifiedusing radiation-sensitive color indicators known as RadTags. Onceapplied to the blood bags, these labels give positive, visualverification of irradiation provided when a minimum of 25 gray (Gy) hasbeen received. For example, after irradiation, a human operator visuallychecks the color on each tag to verify that the blood is sufficientlyirradiated. However, this non-quantitative approach makes it difficultfor a human operator to ascertain whether or not the blood in the bloodbag under irradiation has received over 50 Gy, a maximum recommendeddosage, thereby resulting in operational and cost inefficiencies. It isevident from the current state of art that work is yet to be done on thedesign of wireless X-ray dosimeters that control and automate theirradiation process and alleviate the limitations found in the currentlyused technology, such as wastage of blood, handling errors, anduncertainties of the exact X-ray dose received.

Moreover, the challenge surrounding antenna design has to do with theenvironment and medium in which it has to operate. The presence of theblood bags around radio frequency (RF) waves will result in significantattenuation of the signals due to the highly lossy nature of the bloodcontent. This requires a solution which can shield the electromagneticwaves from the blood.

Therefore, there is a need for improvements in antenna structures foruse with the sensors to realize improved gain and impedance performanceupon placement on lossy structures. Thus, a flexible and efficientantenna structure for wireless power transfer and readout in the fieldof X-ray dosimetry RFID wireless dosimeter chip and tag devices, such asfor use in measuring an amount of radiation delivered to blood by ablood irradiation system, addressing the aforementioned problems isdesired.

SUMMARY OF INVENTION

Embodiments of artificial magnetic conductor (AMC) backed flexibleantennas for a radiation dosimeter, such as an X-ray dosimeter, and ofmethods for detecting radiation dose are described.

Embodiments of a flexible artificial magnetic conductor (AMC)-backedantenna for a wireless radiation dosimeter, such as an X-ray dosimeter,are described. An embodiment of an AMC-backed flexible antenna, forexample, comprises a dipole antenna, and at least one AMC unit cellcommunicatively associated with the dipole antenna, wherein each AMCunit cell comprises a top layer including a metallization pattern, thetop layer configured as a partially reflective surface to reflectelectromagnetic waves of a frequency other than a predeterminedfrequency of interest, a bottom conductive ground plane layer configuredto reduce, prevent or substantially prevent propagation ofelectromagnetic waves at the predetermined frequency of interest and toreflect the electromagnetic waves at the predetermined frequency ofinterest, and a middle layer comprising a foam material configured toprovide a predetermined phase delay between the electromagnetic waves ofthe predetermined frequency of interest from the top layer and thereflected electromagnetic waves of the predetermined frequency ofinterest from the ground plane layer to reduce, prevent or substantiallyprevent phase reversal of electromagnetic waves at the predeterminedfrequency of interest.

In embodiments, methods for detecting the radiation dose of X-raysdelivered to a blood bag are described. An embodiment of a method fordetecting and measuring a radiation dose delivered to a blood bag, forexample, includes the steps of: applying to a specific blood bag awireless dosimeter chip-enabled tag having a predeterminedidentification (ID) value corresponding to a specific blood bag, thewireless dosimeter chip-enabled tag being communicatively associatedwith an AMC-backed flexible antenna, the AMC-backed flexible antennaincluding a dipole antenna, and at least one artificial magneticconductor (AMC) unit cell communicatively associated with the dipoleantenna, wherein each AMC unit cell includes a top layer including ametallization pattern, the top layer configured as a partiallyreflective surface to reflect electromagnetic waves of a frequency otherthan a predetermined frequency of interest, a bottom conductive groundplane layer configured to substantially prevent propagation ofelectromagnetic waves at the predetermined frequency of interest and toreflect the electromagnetic waves at the predetermined frequency ofinterest, and a middle layer comprising a foam material configured toprovide a predetermined phase delay between the electromagnetic waves ofthe predetermined frequency of interest from the top layer and thereflected electromagnetic waves of the predetermined frequency ofinterest from the ground plane layer to substantially prevent phasereversal of electromagnetic waves at the predetermined frequency ofinterest; irradiating blood in the specific blood bag with 25 gray (Gy)to 50 Gy of radiation from an X-ray source; transmitting from a reader amodulated radio frequency signal including the predetermined frequencycontaining the predetermined ID value to the wireless dosimeterchip-enabled tag having the predetermined ID value; receiving themodulated radio frequency signal containing the predetermined ID valueby the AMC-backed flexible antenna communicatively associated with thewireless dosimeter chip-enabled tag having the predetermined ID value;transmitting from the wireless dosimeter chip-enabled tag having thepredetermined ID value to the reader the modulated radio frequencysignal reflected by the AMC-backed flexible antenna includinginformation corresponding to a radiation dose delivered to the specificblood bag; receiving, by the reader, the reflected modulated radiofrequency signal from the wireless dosimeter chip-enabled tag includingthe information corresponding to the radiation dose delivered to theblood in the specific blood bag; and determining, using the reader, fromthe received information, an amount of the radiation dose delivered tothe blood in the specific blood bag associated with the wirelessdosimeter chip-enabled tag having the predetermined ID value.

However, the antenna of the flexible antenna, in embodiments, inaddition to being a dipole antenna, can also be other of suitableantennas, such as a monopole antenna, or a phased array antenna, as candepend on the use or application, and should not be construed in alimiting sense.

These, and other features of the invention, will become more apparentfrom the following specification and drawings, in which reference ismade to the appended drawings, illustrating embodiments of theinvention, by way of example only.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system-level diagram illustrating embodiments of a systemand a method for determining an amount of delivered radiation dose toblood bags each associated with a wireless X-ray dosimeter chip-enabledtag having the predetermined ID, according to the present invention.

FIG. 2 is a system-level diagram illustrating an embodiment of awireless dosimeter chip-enabled tag having a predetermined ID valueassociated with an AMC-backed flexible antenna and the sub-modules ofthe wireless dosimeter chip-enabled tag, according to the presentinvention.

FIG. 3 shows a layout of an embodiment of an AMC-backed dipole antennaaccording to the present invention.

FIG. 4A shows a top view of an embodiment of a 2.45 GHz AMC square loopunit cell, according to the present invention.

FIG. 4B shows a side view of an embodiment of the 2.45 GHz square loopunit cell illustrated in FIG. 4A, according to the present invention.

FIG. 5 depicts a graphic representation of a reflection phase and amagnitude response of an embodiment of a simulated AMC unit cell for anormal incident plane wave, according to the present invention.

FIG. 6 depicts a graphic representation of a simulated peak gain and abeam width at 2.45 GHz with increasing unit cells for an embodiment ofan initial dipole-AMC-backed antenna structure, according to the presentinvention.

FIG. 7 shows a graphic representation of a simulated resonant frequencyand a front-to-back ratio at 2.45 GHz with increasing number of AMC unitcells for the embodiments of initial dipole-AMC antenna structures,according to the present invention.

FIG. 8 shows a graphic representation of simulated return loss, S₁₁,illustrating a reflection magnitude and a frequency for an initialdipole in free space, and for embodiments of an initial dipole-AMCantenna structure and a final dipole-AMC antenna structure, according tothe present invention.

FIG. 9A shows a representation of a simulated radiation pattern and ameasured radiation pattern of an embodiment of an AMC-backed dipoleantenna in the E-plane (XY), at 2.45 GHz, according to the presentinvention.

FIG. 9B shows a representation of a simulated radiation pattern and ameasured radiation pattern of the embodiment of the AMC-backed dipoleantenna of FIG. 9A in the H-plane (YZ) at 2.45 GHz, according to thepresent invention.

FIG. 10 shows a graphical representation of a simulated and a measuredreturn loss, S₁₁, illustrating a reflection magnitude and a frequencyfor an embodiment of an AMC-backed dipole antenna, according to thepresent invention.

FIG. 11 shows a graphical representation of a measured return loss, S₁₁,illustrating a reflection magnitude and a frequency for an embodiment ofan embodiment of an AMC-backed dipole antenna under differentconditions, according to the present invention.

FIG. 12A shows a representation of measured radiation patterns of anembodiment of an AMC-backed dipole antenna in the E-plane (XY) at 2.45GHz under different conditions, according to the present invention.

FIG. 12B shows a representation of measured radiation patterns of anembodiment of an AMC-backed dipole antenna of FIG. 12A in the H-plane(YZ) at 2.45 GHz under different conditions, according to the presentinvention.

FIG. 13 shows an embodiment of an implemented rectenna illustrating a2.45 GHz rectifier and an AMC-backed dipole antenna, according to thepresent invention.

FIG. 14 shows an embodiment of a fabricated AMC-backed dipole antennaaffixed to a blood bag containing a blood mimicking solution, accordingto the present invention.

FIG. 15 shows a diagrammatic illustration of an embodiment of ameasurement setup of the 2.45 GHz rectenna, including a 2.45 GHzrectifier and an AMC-backed dipole antenna in communicating relationwith a reader including a probe apparatus, according to the presentinvention.

FIG. 16 shows a graphic illustration of realized output voltages of anembodiment of a rectenna including a rectifier and an AMC-backed dipoleantenna for varying distances from a transmitting antenna of a readerapparatus, according to the present invention.

FIG. 17 shows a graphic representation of realized output voltages of arectifier from on-chip measurements and projected output voltages of anembodiment of a rectenna including a 2.45 GHz rectifier and anAMC-backed dipole antenna, for varying input powers, according to thepresent invention.

Unless otherwise indicated, similar reference characters denotecorresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION

Embodiments of the disclosure relate to designs of a flexible dipoleantenna including one or more artificial magnetic conductor (AMC) unitcells for use with a RFID wireless dosimeter chip-enabled tag, such ascan be applied to blood bags, that are to be irradiated by a radiationsource, such as an X-ray source, and to methods for determining theradiation dose measured by an RFID wireless dosimeter chip-enabled tagcommunicatively associated with an AMC-backed antenna using a dosimeterreader that communicates with the RFID wireless dosimeter chip-enabledtag via the flexible AMC-backed antenna, such as a flexible AMC-backeddipole antenna. However, the antenna of the flexible antenna, inaddition to being a dipole antenna, can also be other of suitableantennas, such as a monopole antenna, or a phased array antenna, as candepend on the use or application, and should not be construed in alimiting sense.

The term “irradiation”, as is used herein, can include, but is notlimited to the conventional meaning of the term “irradiation”, i.e.,exposure to high energy charge particles, e.g., electrons, protons,alpha particles, etc., or electromagnetic radiation of wave-lengthsshorter than those of visible light, e.g., gamma rays, X-rays,UltraViolet, etc.

Also, as used herein, the term “antenna” for example, can refer to aconductive interface communicatively associated with a receiver or atransmitter, or both, through which electromagnetic waves, fields orsignals, such as radio frequency, microwave or satellite signals orwaves, are received or transmitted. Waves or signals that are radiofrequency fields can be transmitted through the antenna or be associatedwith a transducer that converts radio frequency (RF) fields into highfrequency current or vice versa. There are typically two basic antennatypes: a receiving antenna, such as an antenna which intercepts RFenergy and delivers a current/voltage to the electronic equipment, and atransmitting antenna, which is fed with a current/voltage excitationfrom electronic equipment and generates an RF field or wave fortransmission. Thus the same antenna design can be used as a transmittingand a receiving antenna.

Further, as used herein, for example, the term “dosimeter” refers to adevice used to measure an absorbed dose of ionizing radiation.

Also, as used herein, the term “ionizing radiation” refers to any ofvarious particulate or electromagnetic radiation that is capable ofdissociating atoms into a positively and negatively charged ion pair.

Further, as used herein, the term “foam material” refers to a polymericfoam material in solidified form, formed from polymers. Polymeric foammaterials can include, for example, Polyurethane (PUR or PU) foam, orother suitable foam materials as can depend on the use or application,and should not be construed in a limiting sense.

Also, as used herein, an Artificial Magnetic Conductor (AMC) is anartificial, metallic electromagnetic structure as can be, for example, atype of electromagnetic band gap material or a type of syntheticcomposite having a magnetic conductor surface realized using electricalconductor patterns on a surface suitable for a predetermined range offrequencies, such as a type of implemented metamaterial as can be usedin several antennas and microwave design applications, for example. TheAMC, by utilizing the characteristics of metamaterials in a unit cell,which do not exist naturally, can enhance the performance of variousantenna devices, such as to modify the antenna's radiation pattern andcontrol wave propagation at certain frequencies, as can provide afrequency selective surface, such as at radio frequency and microwavewavelengths, as can be desirable in various antenna applications.

Further, as used herein, inkjet printing as can be used in forming theantenna or the metallization of the AMC, or both, is a type of computerprinting that re-creates a digital image by propelling droplets of ink,as can be a metallized or conductive ink material, onto paper, plastic,or other substrates.

In an embodiment, the flexible antenna desirably includes a dipoleantenna, or can include other suitable antennas, such as a monopoleantenna, or a phased array antenna, and at least one AMC unit cell,wherein the at least one AMC unit cell includes a top layer including ametallization pattern configured to partially act as a reflectivesurface to reflect electromagnetic waves of a frequency other than apredetermined frequency of interest; a bottom conductive ground planelayer configured to reduce, prevent or substantially prevent propagationof electromagnetic waves at the predetermined frequency of interest andto reflect the electromagnetic waves at the predetermined frequency ofinterest, and a middle layer comprising a foam material configured toprovide a predetermined phase delay between electromagnetic waves at thepredetermined frequency of interest from the top layer and the reflectedwaves at the predetermined frequency of interest from the ground planelayer to reduce, prevent or substantially prevent phase reversal at apredetermined frequency of interest.

In an embodiment, in the flexible antenna, the middle layer comprisingthe foam material is configured of a suitable material and dimensions soas to pass the electromagnetic waves at the frequency of interestwithout phase reversal at a predetermined frequency of interest.

In an embodiment, in the flexible antenna, a distance between the toplayer and the bottom conductive ground plane layer can be in the rangeof about 5 mm to about 15 mm.

In another embodiment, in the flexible antenna, the AMC furthercomprises a plurality of unit cells, with the metallization pattern onthe top layer of each unit cell comprising a conductive ink therebyproviding the antenna, desirably a dipole antenna, wherein theconductive ink is printed on the top layer by an inkjet printer. Theconductive ink can comprise silver nanoparticles or other suitableconductive material, as can depend on the use or application, and shouldnot be construed in a limiting sense. The plurality of unit cells canprovide gain to signals received or transmitted by the flexible antennawhile facilitating maintaining good radiation characteristics.

In another embodiment, in the flexible antenna, the unit cells desirablyinclude a plurality of square loop cells arranged in n rows×m columnsarrays on the top layer of the AMC. The square loop cells are spaced atleast 1 mm apart for each other.

In another embodiment, in the flexible antenna, the top layer and thebottom conductive ground plane layer of the AMC include or are formed ofa poly (4,4′-oxydiphenylene-pyromellitimide) material, such as Kapton®or other suitable flexible film, as can depend on the use orapplication, for example, as well as include a conductive material, suchas a conductive metallization, such as can be formed by a conductive inkmaterial.

In another embodiment, in the flexible antenna, including the AMC andthe dipole antenna structure, operates at a bandwidth in the range of2.32 GHz to 2.56 GHz. Desirably, such as for blood irradiationapplications, the AMC-backed dipole antenna structure operates at abandwidth of 2.45 GHz (Giga-hertz). The flexible antenna can further becommunicatively associated with a rectifier, as an energy harvestingdevice, configured to convert radiofrequency energy into electricalenergy, such as a direct current (dc) corresponding to the receivedsignal, and with an energy storage device, such as a capacitor, as canbe included in a dosimeter chip structure or tag, for example.

In an exemplary embodiment, a dosimeter chip structure communicativelyassociated with embodiments of a flexible antenna can be positioned inassociation with a blood bag, as can include a bag member to hold bloodto be irradiated to measure an amount of radiation dose delivered toblood in the blood bag. The dosimeter chip structure includes a flexibleantenna including a dipole antenna communicatively associated with anAMC-backed structure, wherein the AMC-backed structure includes a toplayer including a metallization pattern, the top layer configured as apartially reflective surface to reflect electromagnetic waves of afrequency other than a predetermined frequency of interest, a bottomconductive ground plane layer including a conductive material as aground configured to reduce, prevent or substantially preventpropagation of electromagnetic waves at the predetermined frequency ofinterest and to reflect the electromagnetic waves at the predeterminedfrequency of interest, and a middle layer comprising a foam materialconfigured to provide a predetermined phase delay between theelectromagnetic waves of the predetermined frequency of interest fromthe top layer and the reflected electromagnetic waves of thepredetermined frequency of interest from the ground plane layer toreduce, prevent or substantially prevent phase reversal ofelectromagnetic waves at the predetermined frequency of interest,wherein the flexible antenna is configured to transmit information abouta radiation dose delivered to blood in the specific blood bag to areceiver, such as when interrogated by a reader or a probe by a signalreceived by the antenna, such as the dipole antenna, to transmit theinformation about the radiation dose delivered to the blood in thespecific blood bag.

In other embodiments, methods of detecting a radiation dose include:applying to a specific blood bag a wireless dosimeter chip-enabled taghaving a unique or predetermined ID value corresponding to the specificblood bag, the wireless dosimeter chip-enabled tag being communicativelyassociated with an AMC-backed flexible antenna, the AMC-backed flexibleantenna comprising a dipole antenna, or other suitable antenna, and anAMC-backed structure, wherein the AMC-backed structure includes a toplayer configured to include a metallization pattern to partially act asa reflective surface, a bottom conductive ground plane layer including aconductive material as a ground configured to reduce or preventpropagation of incident electromagnetic waves and to reflect theelectromagnetic waves, and a middle layer including a foam materialconfigured to provide an appropriate or predetermined phase delaybetween incident electromagnetic waves from the top layer and thereflected waves from the ground plane layer; irradiating blood in thespecific blood bag with 25 Gy to 50 Gy of radiation from an irradiationsource, such as an X-ray source; transmitting from a reader a modulatedradio frequency signal containing the unique or predetermined ID valueto the flexible antenna communicatively associated with the wirelessdosimeter chip-enabled tag attached to the specific blood bag;transmitting from the wireless dosimeter chip-enabled tag having thepredetermined ID value to the reader the modulated radio frequencysignal reflected by the AMC-backed flexible antenna includinginformation corresponding to a radiation dose delivered to the blood inthe specific blood bag; and determining, using the reader, from thereceived information, an amount of the radiation dose delivered to theblood in the specific blood bag associated with the wireless dosimeterchip-enabled tag having the unique or predetermined ID value. The methodof detecting a radiation dose can further include the readerdemodulating the received radio frequency signal containing the uniqueor predetermined ID value associated with the wireless dosimeterchip-enabled tag and associated with the specific blood bag andassociating the unique or predetermined ID value and the receivedinformation with its own or another ID value. The emitted modulatedsignal desirably carries information about a sensed radiation dose, suchas an X-ray dose, and a sensed temperature of the blood in the specificblood bag but can carry other or different information, as can depend onthe use or application, and should not be construed in a limiting sense.The radio signal desirably can operate at a frequency of about 2.45 GHz,but can operate at other suitable frequencies, as can depend on the useor application, and should not be construed in a limiting sense.

The following examples are provided by way of illustration to furtherillustrate the exemplary embodiments of antennas for use with an X-raywireless dosimeter chip-enabled tag for blood bags and a method ofdetecting radiation with a dosimeter reader. However, the embodiments ofthe AMC-backed antenna and associated wireless dosimeter chip-enabledtags can have other uses or applications, such as for measuringtemperature or other parameters or quantities in other processes orapplications, and therefore such examples are not intended to limit itsscope or application.

FIG. 1 is a system-level diagram illustrating embodiments of a systemand a method for determining an amount of delivered radiation dose toblood bags each associated with a wireless X-ray dosimeter chip-enabledtag having the predetermined ID. In an exemplary embodiment of FIG. 1,there is shown a system-level diagram 100 for determining an amount of adelivered radiation dose to blood in blood bags including a wirelessdosimeter chip-enabled tag 101, such as for measuring a radiation dosefrom X-rays, in communication with a specific blood bag 105, a pluralityof blood bags 105 and associated wireless dosimeter chip-enabled tags101 being illustrated in FIG. 1, housed inside an irradiation apparatus113, such as a Raycell MK2 Blood Irradiator.

The RFID wireless dosimeter chip-enabled tags 101 are applied tocorresponding specific blood bags 105 and the blood bags 105 associatedwith the RFID wireless dosimeter chip-enabled tags 101 are then placedin an irradiation canister 115 of the irradiation apparatus 113. Eachwireless dosimeter chip-enabled tag 101 has an identification (ID) valuecorresponding to a specific blood bag 105. The irradiation apparatus 113includes an inner canister 103 that houses the blood bags 105 includingthe blood to be irradiated. The irradiation canister 115 and theirradiation apparatus 113 can also include an RF opening or portal 107through which the RFID wireless dosimeter chip-enabled tags 101 throughan associated AMC-backed antenna 102 can communicate with a dosimeterreader 117. An amplitude-shift keying (ASK) signal (Tag ID 2.45 GHz RFsignal) 111 is transmitted from the dosimeter reader 117 though anantenna 119. The signal transmitted from the dosimeter reader 117, suchas a modulated radio frequency signal, contains the predetermined IDvalue corresponding to the wireless dosimeter chip-enabled tag 101associated with the predetermined ID value. After receipt of the signal111 from the dosimeter reader 117 received by the correspondingAMC-backed antenna 102, a back scattered signal 109 from thecorresponding wireless dosimeter chip-enabled tag 101 associated withthe predetermined ID value containing the information from therespective wireless dosimeter chip-enabled tag 101 is transmitted by therespective AMC-backed antenna 102 and received by the antenna 119 of thedosimeter reader 117. The received back scattered signal 109 containingthe information or data corresponding to a specific blood bag 105 isread by the dosimeter reader 117.

The dosimeter reader 117 is placed at a suitable distance from theirradiation apparatus 113, as can depend on the use or application, suchas typically at a maximum distance of up to 1 meter (m), from theirradiation apparatus 113, to receive the radiation dosage measured bythe wireless dosimeter chip-enabled tags 101 associated with thespecific blood bags 105 having the respective predetermined ID values.The dosimeter reader 117 can store or can read out, such as wirelesslythrough the antenna 119 or through a wired connection, the informationor data in the respective received backscatter signals 109 from thecorresponding wireless dosimeter chip-enabled tags 101, such as themeasured radiation dose respectively applied to blood in the specificblood bags 105, or other applicable data for the blood in the specificblood bag 105, such as the temperature of the blood irradiated, time ofirradiation or other applicable information or data, for example.

The exemplary 2.45 GHz X-ray wireless dosimeter chip-enabled tag 101 andthe associated AMC-backed antenna 102 is intended to replace or is asubstitute for the aforementioned color indicator RadTag labels. The2.45 GHz wireless dosimeter chip-enabled tag 101 is typically used as asemi-passive RFID tag employing backscatter modulation and wirelesspower transfer to facilitate minimal power consumption and a low-formfactor. The wireless dosimeter chip-enabled tag 101 associated withembodiments of the AMC-backed antenna 102 desirably includes an energyharvesting unit, such as a rectifier and a capacitor—for self-poweredoperation.

Also, embodiments of the wireless dosimeter chip-enabled tag 101 includea suitable sensor, such as a FGMOSFET sensor, which senses the receivedradiation dosage to the blood bag 105, signal processing electronics,such as a suitable processor and associated memory, that convertmeasured data to pulses and a transmitter or modulator that sends thepulses through the AMC-backed antenna 102 to the dosimeter reader 117operating in the same frequency band. Similar to the RadTag labels, thewireless dosimeter chip-enabled tags 101 and the associated AMC-backedantenna 102 are to be applied to the blood bags 105 as schematicallydepicted in FIG. 1. Embodiments of the AMC-backed antenna, such as theAMC-backed antenna 102, desirably are compact, conform relatively easilyto the wireless dosimeter chip-enabled tag, such as the wirelessdosimeter chip-enabled tag 101, have efficient antenna performance on alossy host structure (such as blood products), and have adequatewireless power transfer operation when implemented in a rectennaconfiguration. The wireless dosimeter chip-enabled tags 101 desirablyare configured to communicate with the RF reader, such as the dosimeterreader 117, typically at a maximum distance of one meter for bloodirradiation measurements, for example. Also, it is desirable that powerconsumption of the wireless dosimeter chip-enabled tag 101 is estimatedto consume a power of 263 microwatts (μW) with a nominal supply of 1.2volts (V), for example, although the power consumed can depend on theuse or application, and should not be construed in a limiting sense.

FIG. 2 is a system-level diagram illustrating an embodiment of awireless dosimeter chip-enabled tag 101 having a predetermined ID valueassociated with an embodiment of the AMC-backed flexible antenna 102 andthe sub-modules of the wireless dosimeter chip-enabled tag 101. In theexemplary embodiment of FIG. 2, there is illustrated the system-leveldiagram of a RFID wireless dosimeter chip-enabled tag 200 and itssub-modules, as an exemplary embodiment of the wireless dosimeterchip-enabled tag 101, and as implemented in a 130 nanometer (nm)complementary metal oxide semiconductor (CMOS) process, for example. Thedosimeter of the RFID wireless dosimeter chip-enabled tag 200 isrealized in a semi-passive RFID (radio frequency identification) tagconfiguration employing backscatter and a wireless RF energy harvestingmodule for low-power operation and low-form factor.

The wireless dosimeter chip-enabled tag 200 is uniquely identified by anID value which is desirably hard-coded into the tags integrated circuit(IC). The wireless dosimeter chip-enabled tag 200 includes an AMC-backedantenna 205, as an exemplary embodiment of the AMC-backed antenna 101,to receive an ASK signal 201 and to transmit a PSK backscattered signal203. The ASK signal 201, such as a constant wave radio frequency (CW RF)signal, is transmitted via the AMC-backed antenna 205 to a demodulator221 to demodulate the received ASK signal 201 and is coupled with adecoder 219 to decode the received ASK signal 201 and an oscillator 217to generate signals for operation of the wireless dosimeter chip-enabledtag 200. The decoder 219 is in communication with a Tag ID 213, whichincludes a unique or predetermined ID value associated with the wirelessdosimeter chip-enabled tag 200. The TAG ID 213 is in communication witha signal processing engine (SPE) 209, or other suitable processor,including or associated with a memory for programs, instructions or datastorage for operation and control of the wireless dosimeter chip-enabledtag 200, such for processing, transmitting or receiving requests, dataor information in or by the wireless dosimeter chip-enabled tag 200. TheSPE 209 is coupled to a modulator 207 which modulates and formats aninformation or data signal, such as the PSK backscatter signal 203, fortransmission from the AMC-backed antenna 205 to a receiver, such as tothe dosimeter reader 117.

The wireless dosimeter chip-enabled tag 200 further desirably includes atemperature sensor 211 to sense the temperature of an object, fluid orother medium associated with the wireless dosimeter chip-enabled tag200, such as blood in the blood bag 105 being irradiated, an energyharvester 223 which harvests the energy from the received ASK signal 201which is in communication with an energy storage module 225 to store theenergy from the received ASK signal 201, which is in turn incommunication with a radiation sensor 215 to sense an amount ofradiation delivered to an object, such as blood in the blood bag 105.The components of the wireless dosimeter chip-enabled tag 200 arecommunicatively associated with each other through the SPE 209 toperform the functions and operations of the wireless dosimeterchip-enabled tag 200, such as to determine an amount of radiationdelivered to the blood bag 105. The wireless dosimeter chip-enabled tag200 associated with the AMC-backed antenna 205 can be modified toperform other applications, as can utilize similar components to thosedescribed and additional components for such other applications, forexample. To communicate with a specific wireless dosimeter chip-enabledtag 200, a reader, such as the dosimeter reader 117, transmits the ASKsignal 201, such as an ultra-high frequency (UHF) 2.45 GHz ASK-modulatedsignal 201, containing the unique or predetermined ID value of thewireless dosimeter chip-enabled tag 200 it wishes to interrogate fordata or information, such as the amount of radiation delivered to bloodin a specific blood bag 105, for example.

For example, each wireless dosimeter chip-enabled tag 200, such as thewireless dosimeter chip-enabled tag 101 inside the irradiation apparatus113, such as the Raycell Mk2 irradiator, demodulates the RF signalreceived through the AMC-backed antenna 205 and compares the received IDvalue to its own unique or predetermined ID value. If the ID valuesmatch, the wireless dosimeter chip-enabled tag 200 transmits itspredetermined ID value from the tag ID 213, a sensed X-ray dose from theradiation sensor 215, and measured temperature from the temperaturesensor 211 through the AMC-backed antenna 205 to a receiver, such as thedosimeter reader 117, using backscatter modulation. For example, thedosimeter reader 117 establishes a backscatter link by broadcasting a2.45 GHz CW carrier tone as the ASK signal 201. During uplinkcommunication, the specified wireless dosimeter chip-enabled tag 200modulates its data, such as radiation, temperature and the predeterminedID value, onto this CW carrier signal using PSK modulation, and reflectsthe signal as the PSK backscattered signal 203 back to the dosimeterreader 117. Desirably, the interrogation of the wireless dosimeterchip-enabled tag 200, and the transmission and reception communications,are carried out using embodiments of the AMC-backed antenna, such as theAMC-backed antenna 205 operating at 2.45 GHz, for example.

For an AMC-backed antenna, such as the AMC-backed antenna 205, an idealAMC desirably should be arranged to form an infinite surface, but sucharrangement is, however, impractical due to practical limitations.Therefore, in embodiments of the AMC-backed antenna, such as theAMC-backed antenna 205, it is desirable to optimize a number of AMC unitcells to be used in an antenna design. Therefore, in the design of anAMC-backed antenna, a number of AMC unit cells for the AMC-backedantenna desirably should be optimized to provide a compact configurationthat boosts the gain of the antenna while maintaining good radiationcharacteristics, as can depend on the use or application, for example.

FIG. 3 shows a layout of an embodiment of an AMC-backed dipole antenna300 and an exemplary design of the AMC unit cells. An AMC's performanceis typically indicated by its reflection phase, reflection coefficientand bandwidth. An ideal AMC completely reflects the incident signal withno phase change at its operating frequency, that is S₁₁=1∠0°. TheAMC-backed dipole antenna 300 includes at least one AMC unit cell 302associated with a suitable antenna, such as a dipole antenna 309, andthe AMC-backed dipole antenna 300 in an embodiment for blood irradiationmeasurement applications desirably has an overall length LF of 100 mmand an overall width WF of 20 mm (100 mm by 20 mm).

The dipole antenna 309, such as for blood irradiation measurementapplications, desirably is a 2.45 GHz dipole having an overall length ALof 38.5 mm and a width AW of 3.75 mm (38.5 mm by 3.75 mm) placed over oron a suitable dielectric layer 310 surface, desirably a 100 mm by 20 mmsurface of Kapton® or other suitable flexible film, as can depend on theuse or application, for example. To preserve flexibility, the dipoleantenna desirably is inkjet-printed on a Kapton® 0.12 mm thickdielectric layer 310 using a silver nanoparticle ink. Also, theAMC-backed dipole antenna 300 desirably includes a plurality of AMC unitcells 302 arranged in a plurality of square loop cells and arranged inan n rows×m columns array on the top layer of the AMC in the AMC-backeddipole antenna 300. Desirably, a one by four array of AMC unit cells 302are illustrated in the AMC-backed dipole antenna 300 of FIG. 3, as canbe desirable for blood irradiation measurements. The AMC unit cells 302are desirably square loop cells and are desirably spaced at a distance“W” of at least 1 mm apart from each other in the AMC-backed dipoleantenna 300, although the number, configurations, dimensions and spacingof the AMC unit cells can depend on the use or application and shouldnot be construed in a limiting sense.

Desirably, each of AMC unit cells 302 has a metallization pattern 304,such as formed by a suitable conductive material, such as a conductiveink, and is desirably of a square loop design on a suitable dielectricmaterial, such as Kapton® or other suitable flexible film. Inembodiments of the AMC-backed dipole antenna 300, a loop configurationfor the metallization pattern 304 is used rather than a patch AMC designto facilitate reducing the foam thickness of a foam spacer 305 requiredfor AMC operation at 2.45 GHz and to ensure the least possible amount ofink is used. The foam material for the foam spacer 305 desirably is apolymeric foam material in solidified form, formed from polymers, suchas, for example, polyurethane (PUR or PU) foam, or other suitable foammaterials as can depend on the use or application, and should not beconstrued in a limiting sense.

The foam spacer 305 for the square loop AMC unit cell(s) 302 desirablyis a 9 millimeter (mm) thick foam spacer 305 between two dielectriclayers, a top dielectric layer 308 adjacent to or integral with thedielectric layer 310 and a bottom dielectric layer 303. The topdielectric layer 308 and the bottom dielectric layer 303 are formed of asuitable dielectric material, such as Kapton® or other suitable flexiblefilm. Desirably, each square loop AMC unit cell 302 includes the 9 mmthick foam spacer 305, between the top dielectric layer 308 and thebottom dielectric layer 303 each of Kapton®, or other suitable polyimidematerial, and the top dielectric layer 308 and the bottom dielectriclayer 303 each having a dielectric constant ε_(r)=3.5 and a loss tangenttan δ=0.02, for example.

The AMC-backed dipole antenna 300 also includes a conductive groundplane layer 301 that also forms a bottom layer of each AMC unit cell302. The ground plane layer 301 includes a conductive material,metallization or metallization pattern, desirably formed on a bottomsurface of the bottom dielectric layer 303, such as of Kapton®, toprovide a ground. The bottom dielectric layer 303 as a substrate layeris desirably formed of a suitable material, such as of Kapton®, or othersuitable polyimide material, with the conductive material, metallizationor metallization pattern of the ground plane layer 301 at the bottomdesirably formed of a suitable conductive material, such as a conductiveink, for example, to provide a ground. In embodiments of the AMC-backeddipole antenna 300 and in each AMC-backed unit cell 302, to preserveflexibility, all metallization patterns or metallization of themetallization pattern 304, such as of the square loop, and of theconductive material, metallization or metallization pattern of theground plane 301, and the arms of the dipole antenna 309 are desirablyinkjet-printed on the appropriate Kapton® sheets(4,4′-oxydiphenylene-pyromellitimide) or on sheets of other suitablepolyimide material, using silver nanoparticle ink of conductivityσ=1×10⁷ Siemens per meter (S/m).

FIG. 4A shows a top view of an embodiment of a 2.45 GHz AMC square loopunit cell 302 and FIG. 4B shows a side view of the embodiment of the2.45 GHz square loop unit cell 302 illustrated in FIG. 4A, according tothe present invention. The embodiment of the AMC square loop unit cell302 in FIG. 4A desirably has a generally square configuration, althoughother suitable configurations can be used, as can depend on the use orapplication, and has a side length LU of 20 mm. The metallizationpattern 304, desirably of a square configuration as illustrated in FIG.4A, desirably has an overall length from one outer side to an oppositeouter side LM of 18 mm and a width LW of the pattern of 1 mm, forexample, although the configurations, dimensions and shapes of themetallization pattern can be other of suitable configurations,dimensions and shapes.

In the side view of the embodiment of the 2.45 GHz square loop unit cell302 of FIG. 4B, there is illustrated the metallization pattern 304 onthe top dielectric layer 308 adjacent to or integral with the dielectriclayer 310 and the bottom dielectric layer 303, with the foam spacer 305between the dielectric layers 308/310 and the dielectric layer 303.Desirably, the foam spacer 305 has a thickness LF of 9 mm, for example,such as for use in blood irradiation applications, although the foamspacer 305 can be of other suitable thicknesses, as can depend on theuse or application. In the illustration of FIG. 4B of the AMC squareloop unit cell 302, the ground plane layer 301 having the conductivematerial, metallization or metallization pattern positioned adjacent thedielectric layer 303 completes the schematic illustration of the AMCsquare loop unit cell 302 structure. As shown in FIG. 3, the AMCstructure desirably includes a plurality of AMC square loop unit cells302, which are arranged in n×m arrays; n rows by m columns. such as anarray of 1×4 AMC unit cells 302, each having the structure illustratedin and described with respect to FIGS. 4A and 4B, for example.

FIG. 5 depicts a graphic representation of a reflection phase and amagnitude response of an embodiment of a simulated AMC unit cell, suchas an AMC square loop unit cell 302 for a normal incident plane wave. Inan exemplary embodiment, when impinged by an RF signal at 2.45 GHz, theAMC square loop unit cell has a reflection response shown in FIG. 5, forexample. FIG. 5 illustrates the reflection phase and magnitude responseof the simulated AMC unit cell for a normal incident plane wave. The AMCunit cell has a reflection magnitude and phase of −0.21 dB and 0.160 dB,respectively, and a bandwidth from 2.29 GHz to 2.61 GHz (320 MHz). Thisbandwidth is defined as the frequencies where the reflection phase fallswithin ±45. Within these frequencies, the image currents are in-phasewith the incident currents, hence the incident and reflected waves arenot subjected to significant destructive interference. As a result, theantenna elements can lie directly on the top of the AMC unit cellsurface without being shorted out.

FIG. 6 depicts a graphic representation of a simulated peak gain and abeam width at 2.45 GHz with increasing an amount of AMC unit cells foran embodiment of an initial dipole-AMC-backed antenna structure. Theantenna is simulated to study its impedance and radiationcharacteristics for different numbers of AMC unit cells. For example,the variation in the simulated gain and beam width of the dipole antennadesign for different AMC unit cell configurations is shown in FIG. 6.From the graph of FIG. 6, it is evident that as the number of unit cellsincreases, the antenna gain improves, as expected. However, this trendin the antenna gain ceases beyond 3×4 unit cells, with the gaindecreasing. Consequently, the antenna beam width narrows with theincreasing number of unit cells. This decrease in beam width can beattributed to the increased directivity and gain as the AMC surfaceapproaches a near ideal case.

FIG. 7 shows a graphic representation of a simulated resonant frequencyand a front-to-back ratio at 2.45 GHz with increasing number of AMC unitcells for the embodiments of initial dipole-AMC antenna structures. Aslight shift in the antenna's resonant frequency is observed in FIG. 7when the AMC unit cell is introduced. This can be attributed to theparasitic capacitance introduced by the gap between the dipole antennaand the AMC unit cells. Based on these results, as illustrated in FIG.7, the 1×4 unit cell array of AMC unit cells is desirable for the AMCstructure, since it offers a low profile with considerable gain,sufficient beam width, broadside radiation and, desirably, itsdimensions complement the dipole antenna associated with the AMC unitcells. The front-to-back ratio and the resonant frequency of the designare also shown in FIG. 7.

FIG. 8 shows a graphic representation of simulated return loss, S₁₁,illustrating a reflection magnitude and a frequency for an initialdipole in free space, and for embodiments of an initial dipole-AMCantenna structure and a final dipole-AMC antenna structure. Thesimulated impedance performance, in FIG. 8, shows a change in theantenna's bandwidth from 20.4% to 9.8% and the resonant frequency shiftsfrom 2.45 GHz to 2.05 GHz without and with the AMC antenna structure,respectively. To compensate for the change in the antenna resonantfrequency and to adequately match the antenna structure to the feed, theinitial dipole length is shortened from 57 mm to 38.5 mm (final design).A reduction in the bandwidth of the antenna is caused by the AMCstructure which is the limiting factor in the design of the AMCstructure.

Referring now to FIGS. 9A and 9B, FIG. 9A shows a representation of asimulated radiation pattern and a measured radiation pattern of anembodiment of an AMC-backed dipole antenna in the E-plane (XY), at 2.45GHz and FIG. 9B shows a representation of a simulated radiation patternand a measured radiation pattern of the embodiment of the AMC-backeddipole antenna of FIG. 9A in the H-plane (YZ) at 2.45 GHz. In order toverify the flexibility of an embodiment of a fabricated AMC-backedantenna, such as the AMC-backed dipole antenna 300 having the 2.45 GHzsquare loop unit cells 302, the AMC-backed antenna structure has beencharacterized in a planar mode and under bending by placing it on acurved foam surface. The radiation performance of the AMC-backed antennaunder these conditions is measured using a Satimo StarLab anechoicchamber. The simulated and measured radiation patterns under planarconditions in the E and H planes at 2.45 GHz are illustrated in FIGS. 9Aand 9B where the dashed line represent the measured pattern and the boldline represent the simulated pattern.

It can be observed that embodiments of the dipole-AMC structuresignificantly reduce back radiation compared to the performance of aconventional dipole antenna, which radiates with an omnidirectionalpattern. Under planar conditions, simulated and measured gains of 6.38dBi (decibels relative to isotropic radiator) and 4.37 dBi are obtainedfrom the antenna in the broadside direction, respectively. At 2.45 GHz,the fabricated antenna exhibits a front-to-back ratio of 8.42 dB,thereby adequately isolating the antenna from its host structure.

For example, FIG. 10 shows a graphical representation of a simulated anda measured return loss, S₁₁, illustrating a reflection magnitude and afrequency for an embodiment of an AMC-backed dipole antenna. Acomparison between the simulated and measured S-parameters of theAMC-backed dipole antenna is shown in FIG. 10 where the dashed linesrepresent the measured values and the solid line represents thesimulated result. For a −8 dB (decibel) impedance bandwidth, measuredS₁₁ shows the AMC-backed dipole antenna has a bandwidth ranging from2.16 GHz to 2.52 GHz (14.6%) in the planar configuration, for example.

FIG. 11 shows a graphical representation of a measured return loss, S₁₁,illustrating a reflection magnitude and a frequency for an embodiment ofan embodiment of an AMC-backed dipole antenna under differentconditions, such as where the AMC-backed antenna structure is in planarand bent conditions and on a blood bag. FIG. 12A shows a representationof measured radiation patterns of an embodiment of an AMC-backed dipoleantenna in the E-plane (XY) at 2.45 GHz and FIG. 12B shows arepresentation of measured radiation patterns of an embodiment of anAMC-backed dipole antenna of FIG. 12A in the H-plane (YZ) at 2.45 GHzunder different conditions, such as where the AMC-backed antennastructure is in planar and bent conditions and on a blood bag. However,as illustrated in FIG. 11, FIG. 12A and FIG. 12B, under bending, themeasured S-parameters and radiation pattern of the AMC-backed antennaremain the same as the planar case. This is a highly desirablecharacteristic of any passive microwave component geared toward flexibleapplications in that its performance does not change with bending of theAMC-backed antenna structure, such as when applied to blood irradiationmeasurement applications, for example.

Referring now to FIG. 14, there is illustrated in FIG. 14 an embodimentof a fabricated AMC-backed dipole antenna affixed to a blood bagcontaining a blood mimicking solution. In the exemplary embodiment shownin FIG. 14, an AMC-backed dipole antenna structure 1400, similar incomponents and construction to the AMC-backed dipole antenna 300, asdescribed herein, is then placed on a filled bag member or blood bag1401, such as by being taped by a suitable tape 1402 to the bag memberor blood bag 1401. The AMC-backed dipole antenna structure 1400 includesa one by four array of AMC unit cells 1403, similar in components andconstruction to the AMC unit cells 302, as described herein, and adipole antenna 1404, similar to the dipole antenna 309. The bag memberor blood bag 1401 has inside it a blood mimicking solution 1405 to studythe effects of lossy host structures on the AMC-backed antennaperformance. For antenna testing, a solution mimicking blood'spermittivity and loss tangent at 1.5 GHz (ε_(r)=59.62, σ=1.836 S/m, tanδ=0.3689) is prepared using ethanol (ε_(r)=25), sodium chloride andwater (ε_(r)=81), as the blood mimicking solution 1405. The electricalproperties of the blood-like solution 1405 were measured using SPEAG'sdielectric assessment kit at 1.5 GHz due to the limited frequency rangeof the available kit. The dielectric properties of the solution areexpected not to change significantly at 2.45 GHz.

In the presence of the bag member or blood bag 1401 and the bloodmimicking solution 1405, the measured impedance and radiationcharacteristics of the AMC-backed antenna structure 1400 are shown inFIGS. 11, 12A and 12B, respectively. The measured results in FIGS. 11,12A and 12B for the AMC-backed antenna structure 1400 on the bag memberor blood bag 1401 with the blood mimicking solution 1405 show that theAMC-backed antenna structure 1400 reflection coefficient remainsrelatively unchanged from 2 GHz to 3 GHz regardless of the bendingcondition or the presence of blood in the form of the blood mimickingsolution 1405 (a lossy host structure), with a variation of ±0.7 dB. Themeasured far field gain results show that the AMC-backed antennastructure 1400 maintains a broadside gain of 4.75 dBi and 4.08 dBi underbending and on a blood bag, such as the bag member or blood bag 1401,respectively, thereby exhibiting no significant change in the antennaperformance of the AMC-backed antenna structure 1400. These resultsvalidate the use of an AMC-backed antenna structure under the antenna toisolate it from the lossy environment, such as on a blood bag filledwith blood, for example.

FIG. 13 shows an embodiment of an implemented rectenna illustrating a2.45 GHz rectifier and an AMC-backed dipole antenna. In FIG. 13, afabricated AMC-backed dipole antenna 1301, similar in components andconstruction to the AMC-backed dipole antenna 300, as described herein,is communicatively associated with a suitable rectifier 1303, as knownin the art, for electrical power generation and energy harvesting, theAMC-backed dipole antenna 1301 and the rectifier 1303 being combined toform a rectenna 1300, as shown in FIG. 13. In order to verify thesuitability of embodiments of the designed AMC-backed antenna 1301 inwireless power transfer (WPT) applications, the rectenna 1300 isrealized by integrating the rectifier 1303 with the AMC-backed dipoleantenna 1301, as shown in FIG. 13. The 2.45 GHz rectifier 1303 isimplemented in the IBM 0.13-μm CMOS process and attains a maximum powerconversion efficiency of 49.7% with a load of 25 kΩ. The rectenna 1300provides the integration of the rectifier 1303 with the AMC-backedantenna 1301 to enable energy harvesting from a dedicated RF source.

The rectifier 1303 is mounted on a printed circuit board (PCB), using a28 pin integrated circuit (IC) socket 1309, for example. The socket pinsof the IC socket 1309 are wire bonded to the RF and dc pads of therectifier 1303. The RF pins from the IC socket 1309 are connected to thearms of a dipole antenna 1307 using two small wire extensions and silverepoxy cured at 80° C. overnight. It is important that the length of wireextensions be kept as small as possible so that the change in impedanceis kept at a minimum. A double sided tape is then used to attach the ICsocket 1309 to the AMC-backed dipole antenna 1301 to provide mechanicalsupport to the IC socket 1309 (as illustrated in FIG. 13).

FIG. 15 shows a diagrammatic illustration of an embodiment of ameasurement setup 1500 of the 2.45 GHz rectenna 1300, including a 2.45GHz rectifier 1303 and an AMC-backed dipole antenna 1301 incommunicating relation with a reader including a probe apparatus. Thevarious components described in the measurement setup 1500, unlessotherwise indicated, are known components in the art for their typicallyknown function. The rectenna 1300 of FIG. 13 is tested using themeasurement setup 1500 at 2.45 GHz using a standard horn antenna with again of 6 dBi as the transmitting antenna and the rectenna 1300 as thereceiving element.

As illustrated on FIG. 15, in the power harvester, one port of theVector Network Analyzer (VNA) with a power amplifier 1513 provides powerof a sufficient RF to a transmitting antenna 1508, as can be atransmitting and receiving antenna 1508. The vector network analyzer1511 monitors parameters of system, such as amplitude and phaseproperties, and is coupled with the power amplifier 1513 to providepower for the measurement setup 1500. The resulting incident free spaceRF wave transmitted by the transmitting antenna 1508 is collected by areceiving antenna 1504, as can be a transmitting and receiving antenna1504, such as the AMC-backed dipole antenna 1301, and is delivered to arectifier 1501, such as the rectifier 1303, and converted to a dc outputthat is read on a voltmeter 1503, the AMC-backed dipole antenna 1504 andthe rectifier 1501, forming a rectenna 1506, such as the rectenna 1300of FIG. 13, for example. The transmitting antenna 1508 and the receivingantenna 1504 of the rectenna 1506 are desirably spaced apart at adistance D for wireless transmission and reception as can depend on theuse or application, such as at a distance of about 1 m for bloodirradiation applications, for example. The probe station 1510 as anexemplary reader apparatus includes dual ground-signal-ground (GSG)probes 1509, as a reader in the reader apparatus. The dual GSG probes1509 generate signals as can include information, such as RF signals, totransmit to the rectenna 1506 and to receive information back from therectenna 1506, such as RF signals as can include information, such as atemperature of blood and a radiation dose delivered to blood in bloodirradiation applications, for example. The dual GSG probes 1509 arecoupled with a rectifier 1505 to convert the received signals to a dcoutput that is read on a voltmeter 1507.

Using the measurement setup 1500 of FIG. 15, the rectifier chip, such asthe rectifier 1501, is tested for two cases, namely wireless testing, inwhich case it is integrated with the AMC-backed antenna 1504 to show thepower transfer from a dedicated RF source and, also, the case for theoutput dc voltages being measured on-chip using a direct RF probefeeding. Using the measurement setup 1500, in the first case setup, tocharacterize the rectenna's power harvesting capabilities, thetransmitting antenna 1508 is placed at a fixed location. A 36 dB gainpower amplifier, as the power amplifier 1513 and a VNA, as the vectornetwork analyzer 1511, are used to supply the required RF signal to thetransmitting antenna 1508 thus achieving a maximum transmit power on theorder of 1 Watt (W), for example. A purpose of the power amplifier 1513is to offset the mismatch losses between the receiving antenna 1504 andthe rectifier chip 1501, which are known to be significant. Thus,embodiments of rectenna 1506 are validated as a suitable device, forvarious applications, such as blood irradiation applications, forexample.

To study the dc values realized by the rectifier 1501, the distance Dbetween the transmitting antenna 1508 and the receiving antenna 1504 arevaried for the maximum transmit power. Referring now to FIG. 16, thereis illustrated a graph showing the relationship between the rectifiedvoltage and the distance from the transmitting antenna of realizedoutput voltages of an embodiment of a rectenna, such as the rectenna1506 including the rectifier 1501, and the AMC-backed dipole antenna1504 for varying distances from the transmitting antenna 1508 of areader apparatus, such as the probe station 1510 including the dual GSGprobes 1509. As illustrated in FIG. 16, as the distance D is increased,the dc output voltage reduces until a maximum range of 1 m is reached,where the rectenna 1506 achieves open-circuit voltages of 0.1 millivolts(mV). At the shortest range, the measurement setup 1500 provides amaximum open-circuit voltage of 4.1 mV, for example.

Although these measurements shown by the graph of FIG. 16 evidence thatthe rectenna 1506 does harvest energy when excited by a dedicated RFsource, the values obtained from these measurements appear to suggestpossibly a relatively poor harvesting efficiency. However, the lowvoltage levels (in the mV range) are attributed to the impedancemismatch between the rectifier 1501 and AMC-backed dipole antenna 1504,since no matching network was implemented for the test measurements, andalso likely due to a relatively poor RF-to-dc conversion efficiency ofthe particular rectifier chip employed in the WPT prototype rectenna1300 of FIG. 13, although the best conversion efficiency obtained fromthe measurements was 49.7%. FIG. 17 shows a graphic representation ofrealized output voltages of a rectifier from on-chip measurements andprojected output voltages of an embodiment of a rectenna including a2.45 GHz rectifier and an AMC-backed dipole antenna, such as therectenna 1300. Referring to FIG. 17, the graph shows the on-chip (i.e.,probe-fed) measured output voltages of the best rectifier chip 1303 fromthat run, as well as the corresponding projected rectenna outputvoltages that would have resulted from the wireless power harvestermeasurement setup 1500 of FIG. 15 (based on a calibrated environmentpath loss at 2.45 GHz using the Fris equation). It is therefore expectedthat the rectenna 1300 will produce voltages ranging from 0 V to 1.7 Vacross a 25 kΩ load for received powers between −5 dBm(decibel-milliwatts) and 20 dBm.

Embodiments of a rectenna including an AMC-backed dipole antenna havebeen described, as well as the design and performance characteristics ofa dipole antenna over an AMC structure are described for use in aproposed dosimeter tag, such as for blood irradiation applications.Embodiments of the design and configuration for a rectenna as describedherein provide an AMC structure to facilitate achieve relatively optimalgain and beam width. Embodiments of the dipole-AMC structure desirablyoperate at 2.45 GHz with a bandwidth from 2.32 GHz to 2.56 GHz, and theAMC antenna structure desirably occupies an area of 20 mm×100 mm with anoverall thickness of 9.24 mm.

The AMC antenna structure desirably uses a 1×4 array of AMC unit cellson the AMC surface to significantly improve its broadside gain andreduce its back lobe at its operating frequency. While studies show thatincreasing the number of AMC unit cells could create high gain antennaswith narrow beam width, it was also noted that increasing the AMCbandwidth can have significant implications on the antenna bandwidth.The measured results for the 1×4 array of AMC unit cells desirably showthat the antenna reflection coefficient remains relatively constant from2 GHz to 3 GHz regardless of the bending condition or presence of alossy host structure. The measured far field radiation pattern resultsfurther desirably show that the AMC-backed antenna structure maintains abroadside radiation under bending and on a filled blood bag with a gainvariation of about ±0.7 dBi. When integrated with a 2.45 GHz rectifier,the performance and suitability of the AMC-backed antenna structure aspart of a wireless power unit indicate that the rectenna is capable ofproviding the nominal voltage level needed by the proposed dosimetertag, with projected output dc voltages of up to 1.7 V across a 25 kΩresistor. In addition, the rectenna achieves a range of up to 1 m, suchas is suitable for blood irradiation applications, for example.

Advantageously, embodiments of the AMC-backed antenna structure designcan be appropriate for wearable devices, mounting on lossy hoststructures and for direct integration with wireless power units,biomedical sensing and signal processing chips, as well as for other ofvarious suitable uses and applications. Also, the artificial magneticconductor structure of the AMC-backed antenna is a high impedancesurface reflecting incident electromagnetic waves at the operatingfrequency with ideally no phase reversal, as can thereby facilitatedesirably isolating the antenna from the blood, such as for bloodirradiation applications, for example. Also, the AMC-backed antennastructure has good impedance and radiation properties both in air and onthe blood bag without any significant deviation in performance, forexample.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

We claim:
 1. A flexible antenna, comprising: a dipole antenna; and atleast one artificial magnetic conductor (AMC) unit cell communicativelyassociated with the dipole antenna, wherein each AMC unit cellcomprises: a top layer including a metallization pattern, the top layerconfigured as a partially reflective surface to reflect electromagneticwaves of a frequency other than a predetermined frequency of interest; abottom conductive ground plane layer configured to substantially preventpropagation of electromagnetic waves at the predetermined frequency ofinterest and to reflect the electromagnetic waves at the predeterminedfrequency of interest; and a middle layer comprising a foam materialconfigured to provide a predetermined phase delay between theelectromagnetic waves of the predetermined frequency of interest fromthe top layer and the reflected electromagnetic waves of thepredetermined frequency of interest from the ground plane layer tosubstantially prevent phase reversal of electromagnetic waves at thepredetermined frequency of interest.
 2. The flexible antenna accordingto claim 1, wherein the middle layer comprising the foam materialreflects impinging electromagnetic waves without phase reversal at thepredetermined frequency of interest.
 3. The flexible antenna of claim 1,wherein a distance between the top layer and the bottom conductiveground plane layer is in the range of about 5 mm to about 15 mm.
 4. Theflexible antenna of claim 1, wherein the flexible antenna comprises aplurality of AMC unit cells each having the metallization patterncomprising a conductive ink.
 5. The flexible antenna of claim 4, whereinthe conductive ink comprises silver nanoparticles.
 6. The flexibleantenna of claim 1, wherein the flexible antenna further comprises aplurality of AMC unit cells.
 7. The flexible antenna of claim 6, whereinthe plurality of AMC unit cells each comprise a square loop cell, theplurality of AMC unit cells being arranged in an array of n rows×mcolumns.
 8. The flexible antenna of claim 7, wherein each square loopcell is spaced at least 1 mm apart from an adjacent square loop cell. 9.The flexible antenna of claim 1, wherein the top layer and the bottomconductive ground plane layer comprises poly(4,4′-oxydiphenylene-pyromellitimide).
 10. The flexible antenna of claim9, wherein the foam material of the middle layer is selected from thegroup consisting of a polymeric foam material in solidified form, andPolyurethane (PUR or PU) foam.
 11. The flexible antenna of claim 1,wherein the flexible antenna is configured to operate at a bandwidthhaving a frequency in the range of 2.32 GHz to 2.56 GHz as thepredetermined frequency of interest.
 12. The flexible antenna of claim11, wherein the artificial magnetic conductor structure is configured tooperate at a frequency of 2.45 GHz as the predetermined frequency ofinterest.
 13. The flexible antenna of claim 1, further comprising: arectifier associated with the flexible antenna, the rectifier configuredto convert radiofrequency energy into direct current (dc) correspondingto a received signal.
 14. A flexible antenna, comprising: an antenna;and at least one artificial magnetic conductor (AMC) unit cellcommunicatively associated with the antenna, wherein each AMC unit cellcomprises: a top layer including a metallization pattern, the top layerconfigured as a partially reflective surface to reflect electromagneticwaves of a frequency other than a predetermined frequency of interest; abottom conductive ground plane layer configured to substantially preventpropagation of electromagnetic waves at the predetermined frequency ofinterest and to reflect the electromagnetic waves at the predeterminedfrequency of interest; and a middle layer comprising a foam materialconfigured to provide a predetermined phase delay between theelectromagnetic waves of the predetermined frequency of interest fromthe top layer and the reflected electromagnetic waves of thepredetermined frequency of interest from the ground plane layer tosubstantially prevent phase reversal of electromagnetic waves at thepredetermined frequency of interest.
 15. A blood bag, comprising: a bagmember to hold blood; and a flexible antenna communicatively associatedwith the blood bag, the flexible antenna comprising: a dipole antenna;and at least one artificial magnetic conductor (AMC) unit cellcommunicatively associated with the dipole antenna, wherein each AMCunit cell comprises: a top layer including a metallization pattern, thetop layer configured as a partially reflective surface to reflectelectromagnetic waves of a frequency other than a predeterminedfrequency of interest; a bottom conductive ground plane layer configuredto substantially prevent propagation of electromagnetic waves at thepredetermined frequency of interest and to reflect the electromagneticwaves at the predetermined frequency of interest; and a middle layercomprising a foam material configured to provide a predetermined phasedelay between the electromagnetic waves of the predetermined frequencyof interest from the top layer and the reflected electromagnetic wavesof the predetermined frequency of interest from the ground plane layerto substantially prevent phase reversal of electromagnetic waves at thepredetermined frequency of interest, wherein said flexible antenna isconfigured to transmit information about a radiation dose delivered toblood in the bag member to a receiver.
 16. A method for detecting aradiation dose delivered to blood in a blood bag, comprising: applyingto a specific blood bag a wireless dosimeter chip-enabled tag having apredetermined identification (ID) value corresponding to the specificblood bag, the wireless dosimeter chip-enabled tag being communicativelyassociated with an artificial magnetic conductor (AMC)-backed flexibleantenna, the AMC-backed flexible antenna comprising: a dipole antenna;and at least one AMC unit cell communicatively associated with thedipole antenna, wherein each AMC unit cell comprises: a top layerincluding a metallization pattern, the top layer configured as apartially reflective surface to reflect electromagnetic waves of afrequency other than a predetermined frequency of interest; a bottomconductive ground plane layer configured to substantially preventpropagation of electromagnetic waves at the predetermined frequency ofinterest and to reflect the electromagnetic waves at the predeterminedfrequency of interest; and a middle layer comprising a foam materialconfigured to provide a predetermined phase delay between theelectromagnetic waves of the predetermined frequency of interest fromthe top layer and the reflected electromagnetic waves of thepredetermined frequency of interest from the ground plane layer tosubstantially prevent phase reversal of electromagnetic waves at thepredetermined frequency of interest; irradiating blood in the specificblood bag with 25 gray (Gy) to 50 Gy of radiation from an X-ray source;transmitting from a reader a modulated radio frequency signal includingthe predetermined frequency of interest containing the predetermined IDvalue to the wireless dosimeter chip-enabled tag having thepredetermined ID value; receiving the modulated radio frequency signalcontaining the predetermined ID value by the AMC-backed flexible antennacommunicatively associated with the wireless dosimeter chip-enabled taghaving the predetermined ID value; transmitting from the wirelessdosimeter chip-enabled tag having the predetermined ID value to thereader the modulated radio frequency signal reflected by the AMC-backedflexible antenna including information corresponding to a radiation dosedelivered to the blood in the specific blood bag; receiving, by thereader, the reflected modulated radio frequency signal from the wirelessdosimeter chip-enabled tag including the information corresponding tothe radiation dose delivered to the blood in the specific blood bag; anddetermining, using the reader, from the received information, an amountof the radiation dose delivered to the blood in the specific blood bagassociated with the wireless dosimeter chip-enabled tag having thepredetermined ID value.
 17. The method for detecting a radiation dosedelivered to blood in a blood bag according to claim 16, furthercomprising: demodulating by the reader the received radio frequencysignal containing the predetermined ID value of the wireless dosimeterchip-enabled tag and information corresponding to the radiation dosedelivered to the blood in the specific blood bag.
 18. The method fordetecting a radiation dose delivered to blood in a blood bag accordingto claim 17, wherein the information in the received radio frequencysignal includes a sensed X-ray dose delivered to the blood in thespecific blood bag and a temperature of the irradiated blood in thespecific blood bag.
 19. The method for detecting a radiation dosedelivered to blood in a blood bag according to claim 16, wherein theinformation corresponding to the radiation dose includes a sensed X-raydose delivered to the blood in the specific blood bag and a temperatureof the blood irradiated in the specific blood bag.
 20. The method fordetecting a radiation dose delivered to blood in a blood bag accordingto claim 16, wherein the predetermined frequency of interest of themodulated radio frequency signal operates at a frequency of about 2.45GHz.